1. Field of the Invention
The invention relates to a method for in-situ calibration of quantity measurement of a fluid flowing in a channel, wherein the amount of the fluid flowing through is measured in a per-se known way by a measuring means. The invention has as its subject in apparatus for in-situ calibration of quantity measurement of a fluid flowing in a channel, too, wherein a flow measuring means measuring the volume of the flowing fluid is arranged in a measuring shaft, and the flow measuring means is coupled to a per-se known data collecting and, preferably, data transmitting electronic unit.
The invention relates to solutions on the field of in-situ calibration of quantity measurement of a fluid including a mobile measuring station which provide metrological results with correct certainty without limitations in an economic way. One of the most significant applications of the invention is the certified, calibrated measurement of the volume of sewage water flowing in channels, these measurements having legal relevance.
2. Description of the Related Art
The measurement as in this invention can be described under the terms of hydraulic conditions as a liquid flow with free surface, sometimes as a full-piped or backwatered flow (the sewer pipe may be filled by the sewage flow or the flow may have a backwater effect) and the flow may be a non-permanent one with free outlet; sedimentation may also occur. Under these conditions, continuing and permanent measurement of flow shall be provided.
The hydraulic conditions as described above can be cooped with by flow-meters such as Parti-Mag II induction flow-meter, Parschall or Venturi-type models. The measuring unit is arranged in a measuring shaft and it often has an automatic, programmable cleaning and washing equipment. The measured values such as volume flow, summarised amounts can be registered locally or they can be forwarded to a remote data transfer system. The usual xe2x80x9cblack boxxe2x80x9d of the electronic unit registers the events of the measurement cycle, the operational conditions of the station and it collects measurements data.
It is characteristic for all known solutions that their measuring accuracy cannot be controlled, it is not certified and, further, the measurement methods don""t fulfil the legal conditions of a measurement with legal effect. Thus, these measurements are not only uncertain and inaccurate, but they don""t have legal relevance, therefore, such actions as accounting, taxation, certified fulfilment cannot be based on them.
According to the well known metrological requirement, the flow-meter to be tested shall be compared to a certified standard, the measuring uncertainty of which is three time less than the measuring uncertainty of the flow-meter to be tested. In the state of the art solutions, this requirement cannot be fulfilled, therefore, calibration is carried out nowadays only in laboratories under artificial conditions, in measuring circles operated with water even for sewage flow-meters as well, and not on the site. As it has been proved, the flow-meters calibrated in laboratories (even the sophisticated induction flow-meters) have a drift and uncertainty (or other malfunction) when used as reference flow-meters without the possibility of control. It has also been proved, that the known flow-meters calibrated with conventional methods will never meet the requirements of the legal regulations or the standards given for reference etalons which are required to produce reliable measurements in all and every minute of the measurement. Thus, the known solutions are not suitable for alone-standing calibration under the condition of the relevant rules and standard.
Another method used for in-situ flow-measurement is the so called xe2x80x9cflow profilingxe2x80x9d hydraulic method. In this, the flow rate of an open surface water flow is determined by speed measurement in discrete points of the measurement cross-section of the channel with the help of induction flow-meters or Doppler speed gauges resulting the actual parameters of the spatial speed dispersion and from this and from the simultaneous measurement of the water level, the actual water flow rate can be calculated. These values are then compared to the fluid flow rate values displayed by the flow-meter to be tested.
The flow in channels is a gravitational, non-permanent one with open surface, thus, the instantaneous fluid rates in the measurement cross sections of the controlling flow-meter and the flow-meter to be tested are never identical. The difference depends on the amount of change-in-time of the actual flow, and this deviation cannot be reduced onto an acceptable level in a channel with open surface, as with sewage channels the case is. Therefore and because of reasons arising out of the test arrangement as described above, the measurement uncertainty of the known method is considerably high, and is not lower than that of the flow-meter to be tested. Thus, the above mentioned metrological requirement in respect of the measuring uncertainty cannot be satisfied. It is needless to say, that the back-reference to the national measurement etalons cannot be provided, which counteracts to the calibration requirement.
It is quite disadvantageous with known solutions, that the calibrations are never carried out with the operational liquid (e. g. sewage water). The in-line flow-meter removed from its operational position within the channel and transported into the measurement laboratory often suffers from mechanical damages as well. Further, transportation of the flow-meter to a laboratory for calibration does present a considerable risk of pollution and infection. Out of these facts, legal and technical problems may arise with the known methods, as well.
As it will be clear for now, in the prior art, solutions for in-situ calibration of non-stop flow-meters operated under general hydraulic conditions in open surface channels such as sewage channels, e. g. sewage water flow-meters or other liquid flow-meters didn""t got previously known, which would satisfy the general metrological requirements based on international rules and standards.
The main objective of the present invention is to provide a method for in-situ calibration of quantity measurement of a fluid flowing in a channel, preferably for that of sewage water discharged into gravitational sewage channels, resulting in a certified measuring station with permanent, stable and certain measurement accuracy, with which measurements with legal effect can also be realised. The method and the apparatus realising this method shall both be applicable in all (sewage) channels as seen in the practice and with small, middle and high water outputs during the calibrations, and with all flow-meters as known in the state of the art, regardless on the amount and quality of the liquid to be measured.
The basic idea of this invention is to compare the measuring uncertainty of the operational in-line flow-meter on the site of the measurement to the measuring uncertainty of a calibrated working standard etalon.
Hence, according to the invention, in a method for in-situ calibration of quantity measurement of a fluid flowing in a channel, the amount of the fluid flowing through is measured in a per-se known way by a measuring means.
The improvement of the method is in that the measuring means of the volume of the fluid is disconnected from the fluid flow, measuring fluid is accumulated in a certified and pre-determined amount on site of the calibration, this certified and pre-determined amount of measuring fluid is led through the measuring means with a pre-determined volume flow, in the course of which the volume values measured by the measuring means are saved, then the measured volume values and the calibrated standard real values of the fluid led through is compared to each other and, with this, the quantity measurement of the flowing fluid is calibrated.
The invention has as its subject an apparatus for in-situ calibration of quantity measurement of a fluid flowing in a channel, too, wherein a flow measuring means measuring the volume of the flowing fluid is arranged in a measuring shaft, and the flow measuring means is coupled to a per-se known data collecting and, preferably, data transmitting electronic unit.
The improvement of the apparatus is in that it comprises a calibration tank having a officially certified volume and being erected on site of the measurement, said calibration tank being connected to a source of a measuring liquid as well, at its outlet, to a measuring conduit discharging into said channel before the flow-meter seen in direction of flow of liquid within the channel , before calibration, the calibration tank contains measuring fluid in a pre-determined and certified amount, and the measuring conduit has at least one draw-off valve means for controlling the flow of the measuring fluid in a certified way.
Various optional or preferred features are set out in the detailed description forming part of this specification.
Thus, in one exemplified realisation of the method of this invention, the measuring fluid is led through for more than one time, preferably under different flow velocities and flood wave shapes covering the whole measuring range of the measuring means, wherein the velocity range of the change of the volume flow of the flowing fluid permitted for the given measuring means in the given measuring arrangement is determined by experiments before start of the calibration.
It is still preferable, if the fluid flowing in the channel is used as said measuring fluid, and this fluid is gathered in a previously certified measuring container. The fluid flowing in the channel and used as said measuring fluid can preferably be at least partially substituted or completed by a fluid being available on site of the calibration.
In another preferred realisation, the flow of the measuring fluid is controlled or determined by a certified etalon flow-meter before leading the fluid through the measuring means.
It still preferred, if the flow of the measuring fluid is controlled or determined by a certified etalon flow-meter before leading the fluid through the measuring means.
It is prefreable, if the etalon flow-meter is previously calibrated and certified by flowing through the measuring fluid in a certified standard real volume.
In a preferred realisation, the measuring fluid is led through a measuring conduit having the same hydraulic parameters as the channel and the measuring means is connected into this measuring conduit.
In case of a full-piped measuring means, the measuring fluid can be led through said measuring means with flow parameters deferring from that of the gravitational flow. Therein, the certified amount of measuring fluid can also be determined after its passage through the measuring means.
In one exemplified embodiment of the apparatus this invention, the channel has a provisional gate for sealingly blocking the channel for the time of calibration before the flow-meter seen in direction of flow of liquid within the channel .
It is also preferred, according to the invention, that a by-pass conduit is provided to pass by the gate and the measuring shaft.
A further preferred embodiment is wherein a collection reservoir is provided between the calibration tank and the measuring conduit.
It is still another preferred embodiment, wherein an etalon flow-meter is arranged in the measuring conduit.
A further preferred embodiment is wherein the etalon flow-meter is in direct connection with a source of the measuring liquid with the intervention of at least one filler valve.
It is still another preferred embodiment, wherein the measuring conduit has a free surface downstream tank for outflow after the etalon flow-meter seen in direction of flow of the liquid.
It is also preferred, according to the invention, that the flow-meter removed from the measuring shaft is mounted into a measuring pipe after the free surface downstream tank, and the measuring pipe has the same hydraulic parameters as the channel.
Preferably, a full-piped measuring means is provided and the channel is formed as a pressure conduit and a slide valve disconnecting the measuring means out of the pressure conduit is arranged before the measuring means, and connection fitting introducing the measuring liquid into the pressure conduit, preferably under pressure is provided between the slide valve and the measuring means.
It is still another preferred embodiment, wherein a full-piped measuring means is provided and the channel is formed as a pressure conduit and a slide valve disconnecting the measuring means out of the pressure conduit is arranged after the measuring means, and connection fitting introducing the measuring liquid into the pressure conduit, preferably under pressure is provided between the slide valve and the measuring means.